From: Paolo Bonzini <pbonzini@redhat.com>
To: Andy Lutomirski <luto@amacapital.net>,
Marcelo Tosatti <mtosatti@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
Radim Krcmar <rkrcmar@redhat.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
kvm list <kvm@vger.kernel.org>, Alexander Graf <agraf@suse.de>
Subject: Re: [PATCH] x86/vdso/pvclock: Protect STABLE check with the seqcount
Date: Thu, 7 Jan 2016 22:47:47 +0100 [thread overview]
Message-ID: <568EDD03.6020508@redhat.com> (raw)
In-Reply-To: <CALCETrVarOvbDVSi7AW4ZHge_kCRdtmfc1dNReW64_N3v24=WA@mail.gmail.com>
On 07/01/2016 22:13, Andy Lutomirski wrote:
> I don't understand what you mean.
>
> In the old code (4.3 and 4.4), the vdso checks STABLE_BIT at the end,
> which is correct as long as STABLE_BIT can never change from 0 to 1.
>
> In the -tip code, it's clearly wrong.
>
> In the code in this patch, it should be correct regardless of how
> STABLE_BIT changes as long as the seqcount works. Given that the
> performance cost of doing that is zero, I'd rather keep it that way.
> If we're really paranoid, we could move it after the rest of the pvti
> reads and add a barrier, but is there really any host on which that
> matters?
I agree that your patch is fine.
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Paolo
next prev parent reply other threads:[~2016-01-07 21:48 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-12-20 11:05 [PATCH v2 0/4] x86: KVM vdso and clock improvements Andy Lutomirski
2015-12-20 11:05 ` [PATCH v2 1/4] x86, vdso, pvclock: Simplify and speed up the vdso pvclock reader Andy Lutomirski
2016-01-04 20:26 ` Marcelo Tosatti
2016-01-04 22:33 ` Andy Lutomirski
2016-01-04 22:59 ` Marcelo Tosatti
2016-01-04 23:14 ` [PATCH] x86/vdso/pvclock: Protect STABLE check with the seqcount Andy Lutomirski
2016-01-07 21:02 ` Marcelo Tosatti
2016-01-07 21:13 ` Andy Lutomirski
2016-01-07 21:47 ` Paolo Bonzini [this message]
2016-01-08 14:04 ` Marcelo Tosatti
2016-01-12 19:48 ` Andy Lutomirski
2016-01-13 10:46 ` Ingo Molnar
2016-01-14 9:07 ` [tip:x86/urgent] " tip-bot for Andy Lutomirski
2015-12-20 11:05 ` [PATCH v2 2/4] x86/vdso: Get pvclock data from the vvar VMA instead of the fixmap Andy Lutomirski
2015-12-20 11:05 ` [PATCH v2 3/4] x86/vdso: Remove pvclock fixmap machinery Andy Lutomirski
2015-12-20 11:05 ` [PATCH v2 4/4] x86/vdso: Enable vdso pvclock access on all vdso variants Andy Lutomirski
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